The analgesic effect of nalbuphine and its long-acting prodrug, nalbuphine arachidicate, in rats

Nalbuphine is an opioid-analgesic with agonist-antagonist properties. Recently, we synthesized a nalbuphine prodrug, nalbuphine arachidicate. The aim of the present study was to evaluate the analgesic effect and the analgesic duration of this prodrug. Male Sprague-Dawley rats (n=10 in each group) were used. Nalbuphine arachidicate was prepared in an oily solution dosage form and injected intramuscularly at a dosage of 25 μmol/kg. A nalbuphine HCl solution was injected intramuscularly at a dosage of 25 μmol/kg in the control group. The analgesic effect of nalbuphine arachidicate was assessed using the cold-ethanol tail-flick test (-20°C) and compared with that of nalbuphine HCl. The results show that both nalbuphine arachidicate and nalbuphine HCl demonstrate significant analgesic effects. The analgesic duration of nalbuphine arachidicate (78 h) was much longer than that of nalbuphine HCl (2 h). This fascinating finding is worthy of further evaluation.